ABSTRACT Alumina nanoparticles were synthesized by thermal dehydration of Al(OH)3 (gibbsite), which shows the sequential formation of AlOOH (bohemite), γ, δ, θ, and α-alumina phases upon heat treatment in the temperature range: 150–1150°C. Alumina nanoparticles were characterized by X-ray diffraction and 27Al MAS-NMR studies to investigate the structural transitions, in particular, the changes in Al—O speciation as a function of heat treatment. γ-alumina is produced by annealing bohemite at 400°C, and transforms into α-alumina via the formation of δ and θ-alumina as the intermediate phases. The formation of θ and α-alumina starts at 1020°C and the concentration of these phases increases upon annealing at 1100°C, while the concentrations of γ and δ-alumina decreases steadily. The heat treatment at 1150°C produces α-phase (84%) and the remnant θ-phase (16%). 27Al MAS-NMR revealed the existence of two types of Al—O speciation i.e. AlO4 and AlO6 structural units whose relative concentration depends upon the transition alumina phases.

中文翻译：

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氧化铝纳米粒子的合成及结构表征

摘要 氧化铝纳米颗粒是通过 Al(OH)3（三水铝石）的热脱水合成的，这表明在以下温度范围内热处理后依次形成 AlOOH（波希米特）、γ、δ、θ 和 α-氧化铝相：150– 1150°C。氧化铝纳米粒子通过 X 射线衍射和 27Al MAS-NMR 研究进行表征，以研究结构转变，特别是 Al-O 形态随热处理的变化。γ-氧化铝是通过在400°C下对波希米特进行退火而产生的，并通过形成δ和θ-氧化铝作为中间相转变为α-氧化铝。θ 和 α-氧化铝的形成开始于 1020°C，这些相的浓度在 1100°C 退火后增加，而 γ 和 δ-氧化铝的浓度稳定下降。1150°C 的热处理产生α-相（84%）和残余的θ-相（16%）。27Al MAS-NMR 揭示存在两种类型的Al-O 形态，即AlO4 和AlO6 结构单元，其相对浓度取决于过渡氧化铝相。